One design difference between a central air conditioner and a window unit is that the former is split into two components, with one inside the house and one outside. Window units pack everything into one box. As the heart of the air cooling system, the compressor is a device that pressurizes the liquid refrigerant to a cooler temperature, which results in a cooling of the air flowing around it. This cooler air is injected back into the room.
The condenser in the air conditioning system acts as a dehumidifier. Similar to a miniature radiator, hot, compressed air drawn from the room passes through the condenser, becoming cooler in the process, and drawing the liquid out of it. You can identify the condenser by locating the part of the central unit that has rotating metal fins and is located outdoors. A window unit's condenser is the part at the rear of the compartment where metal slits have been cut on the sides and back of the appliance.
When the refrigerant leaves the condenser, it has transformed from a gas into a liquid. Upon entering the evaporator through a tiny hole, the liquified refrigerant's pressure drops, and it begins to turn back into a gas and evaporate. By that time, it is a cool, low-pressure gas ready to make the return trip to the compressor, where hot air will be passed over it again and the entire process repeated.
Refrigerant able to change states from gas to liquid and back again is the catalyst in a properly working air conditioner. Along with the compressor, condenser and evaporator, this refrigerant works to draw hot air out of the room and expel it outside the house, while at the same time wringing liquid from some of it in order to cool it and put it back into the room. As long as these four elements of the process work together properly, your house should stay cool and comfortable during the long, hot days of summer.